Cumbrian period property overcomes issues of damp and mould in major renovation

Illias Igoumenidis from Ecological Building Systems discusses the transformation of a derelict cottage into a desirable holiday retreat.



hen a purchaser buys a residential property at auction the mantra is usually ‘buyer beware’, particularly if the house in question is a 19th century stone-built cottage located in the notoriously wet and coastal climate of West Cumbria. But when Steven Wooldridge bought Glen Cottage to transform the dilapidated property into a historical haven for rental to holidaymakers, he knew it would be a labour of love, and he also knew just the company to offer him the solutions required to bring the cottage back to life without compromising any of its original character and charm.

Steven explains: “When we bought Glen Cottage, we knew that we had invested in a unique Cumbrian property. It’s one of the oldest houses in Allonby, on the west coast of Cumbria, and was owned for many years by the late eminent local Artist, Percy Kelly. We really wanted to keep the distinctive features and characteristics of the sandstone walls.

“The house was very damp because moisture was trapped by the external cement render, so we decided to remove this and replace it with a ‘breathable’ plaster. We wanted to use materials that are sympathetic to how the walls should perform and were very lucky to find Ecological Building Systems – the sole importers of the Diasen range of thermal plasters – right on our doorstep here in Cumbria. The products have provided the ideal solutions for our refurbishment, and Ecological Building Systems’ advice and support has been invaluable throughout specification and programme delivery.”

Sympathetic solutions

The first step in the refurbishment process was to strip back both the internal and external walls to uncover the full extent of the damp issues with the property and remove the extensive mould that had built up over time. This uncovered beautifully undulating walls that were extremely solid but far from straight.

The choice of thermal plaster was driven both by the desire to keep this authentic rustic aesthetic and also by the need to control moisture levels to prevent future problems with damp and mould. Use of a conventional impervious insulation material would not only have removed the original contours and reduced the internal space; it would also have trapped moisture within the fabric of the building.

Conversely, the Diathonite system of thermal plasters from Diasen offers a diffusion-open solution that skims the surface of the existing solid walls and combines excellent thermal performance with a hygroscopic capacity that absorbs and dissipates humidity, preventing the potential for condensation and mould. The Diathonite Evolution thermal plaster used as part of a combination of breathable solutions from Ecological Building Systems at Glen Cottage is based on a diatomaceous earth formulation, leveraging the high porosity of this naturally occurring mineral – which is capable of absorbing up to 1.5 times its own weight in moisture – to provide high levels of capillarity. Diatomaceous earth is combined with cork particles to enhance thermal resistance and sound absorption, naturally porous and lightweight aerated clay and NHL 3.5 lime, which provides a hydraulic binder for the thermal plaster.

Diathonite Evolution was used as the insulation and resurfacing plaster for both the internal and external walls in a project that focused on maximising the lifespan of the building in addition to improving comfort and delivering an aesthetic that combines heritage and character with contemporary high standards of finish. 50mm of Diathonite was applied internally and 30mm externally, improving the U-value from to 2.5 to 0.45W/m²K.

Eliminating damp

The contractors engaged to carry out the project were experienced in the use of lime renders for heritage properties but had never used the Diasen product range before, so Ecological Building Systems provided training and an induction into installation best practice and product uses and performance.

Work then began on the refurbishment of the two-storey cottage’s interior. After stripping out the existing dry lining, a new damp-proof membrane was installed under the slab and cut flush to the top of the slab and Diasen Watstop, an epoxy waterproofing system suitable for internal or external use, was applied by brush above the slab in continuity with the membrane to create a tanking system that will prevent moisture from rising through the walls from under ground. The Diasen Watstop was allowed to cure until it was semi-dry so that the tacky surface would provide a key for the Diathonite plasters.

To provide a salt barrier and enhanced dehumidification at Glen Cottage, Diathonite Deumix+, a cork-based thermal insulation plaster which includes NHL 5 as opposed to NHL 3.5, was applied to the internal walls in more challenging areas from the level of the slab to 500mm above the top line of the tanking system in 25mm sprayed on layer.

The Diathonite Evolution was spray-applied in two 25mm layers, one per day, creating a total plaster depth of 50mm, and this was then floated by hand to provide a smooth internal wall surface, following the contours of the original walls.

Once the Diathonite plaster was thoroughly dried 10 to 11 days later, a breathable lime-based finishing render was applied directly onto the plaster in two coats. Developed by Diasen specifically for use with Diathonite plaster, Argacem HP has a macroporous structure, which improves the dehumidifying properties of the plaster, supporting the building’s hygrometric balance while helping to eliminate mould thanks to the antibacterial action of lime.

Once the finishing render had dried, the project team applied natural paints onto the new surface to finish the interior walls.

External upgrade

Externally, stripping back the mouldy and discoloured render revealed rubble sandstone which was cleaned and brushed to remove any loose particles but no primer was required due to the naturally rough surface, which provided an ideal key for application of the plaster. For the timber lintels and window surrounds, however, Diasen Aquabond was used to aid adhesion of the Diathonite Evolution to these surfaces.

For scheduling and logistical reasons, the Diathonite Evolution was hand-applied to the external walls, with the grey of the wet thermal plaster gradually turning to white as each surface dried. A cherry picker was used to enable hand application at height on the two-storey building.

Once dried, the hand-applied Diathonite Evolution provided a smooth surface for the application of Diasen D20, a water-based paint primer for use on the plaster. The external walls were then finished with Diathonite Cork Render sprayed by a hopper, a diffusion-open coloured finishing coat that provides both water-repellent and anti-fungal protection to the newly-plastered walls. This enabled a clean, white finish in keeping with the location and original aesthetic of the building.

Complete comfort

Glen Cottage is now completed and available to rent for those looking for a coastal retreat that combines authentic charm and a creative past with a warm, dry, quiet and damp-free interior thanks to the breathability and thermal performance of the Diasen range of thermal plasters and acoustic renders.

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